1. Field of the Invention
The present invention relates to a brake fluid pressure control system for an automotive vehicle, and more particularly to a system or a device for controlling an anti-skid operation of the vehicle to make the vehicle stop quickly and safely at a braking operation.
2. Description of Related Art
An anti-skid control device has hitherto been known in which skidding conditions of wheels of an vehicle are detected and brake fluid pressures in the wheel cylinders are controlled so that the pressures are decreased, increased or maintained according to detected skidding conditions. Usually, a slip ratio of the wheels relative to a road surface is controlled in a range from 10% to 20% so that the vehicle is stopped quickly and safely at a braking operation. In this kind of system, when a rotational speed of a wheel becomes lower than a predetermined level and a deceleration of the wheel is larger than a predetermined value, the brake fluid pressure is decreased by means of an electromagnetic valve controlled by a computer, because it is judged that the wheel tends to be locked under those conditions.
The wheel speed and the deceleration, however, may be affected by a condition of the road surface, particularly by its roughness or a momentary decrease of its friction coefficient. Therefore, the braking pressure in the wheel cylinder may be decreased at an improper time according to inadequate information being sensed. This may result in a larger amount of brake fluid consumption in the wheel cylinders, a noise level increase in a pump for returning the brake fluid to a master cylinder and an increased amount of a kick-back of a brake pedal.